Recently development of a display device using three primary color laser light is progressing because of good color reproducibility and low power consumption. A laser light, on the other hand, is a monochromatic light, and wavefronts are coherent, hence if a laser is focused on one point of a retina when it enters a human eye, the retina may receive negative influence. Therefore, with respect to products that use a laser light, based on International Standard IEC 60825, or JIS C6802:2005 in Japan, laser products are classified and guidelines are provided for each class that manufacturers and users should adhere to, and only a laser product that conforms to the standard is manufactured.
According to JIS C6802:2005, a term maximum permissible exposure (MPE) is specified, and the level of laser radiation, which does not cause undesirable influence on the human body, even if the human body is exposed to radiation under a normal environment, is designated using the laser wavelength, size of light source, exposure time, tissue exposed to a laser light, laser pulse width or the like as parameters. Manufacturers of laser products have the duty to produce laser products strictly adhering to these standards.
An example of a display device using a laser light is a display device which can perform stereoscopic display to the naked eye (e.g. see Patent Document 1). Configuration and principle of the display device using a laser light will now be described with reference to drawings.
FIG. 11 is a perspective view depicting a conventional display device. A laser light emitted from a laser light source 103 enters a side face of a light guiding plate 102 via an optical fiber 104, is diffused in the light guiding plate 102, and is emitted approximately in the vertical direction from a principal plane of the light guiding plate 102. A deflecting unit 105 deflects a traveling direction of the laser light emitted from the light guiding plate 102, and causes the laser light to enter a liquid crystal panel 101. The liquid crystal panel 101 is controlled by a controller 107 and modulates the laser light according to an image signal to be displayed. A stereo camera 106 captures an image of an observer (not illustrated) who observes the liquid crystal panel 101.
The controller 107 recognizes a relative positional relationship of the pupils of the observer and the display device based on an image captured by the stereo camera 106. After recognizing the positions of the pupils of the observer, the controller 107 controls the deflecting unit 105 so that the laser light transmitted through the liquid crystal panel 101 enters only the right eye of the observer in a state where a parallax image for the right eye is displayed on the liquid crystal panel 101. Then the controller 107 controls the deflecting unit 105 so that the laser light transmitted through the liquid crystal panel 101 enters only the left eye of the observer in a state where a parallax image for the left eye is displayed on the liquid crystal panel 101. A stereoscopic display is implemented by repeating the cycle for the left eye and the right eye as described above. If a same image is displayed for the left eye and the right eye, an ordinary display device that displays plane images is implemented.
FIGS. 12A and 12B are cross-sectional views sectioned at the B-B line in FIG. 11. In FIGS. 12A and 12B, a same composing element as FIG. 11 is denoted with a same reference numeral, for which description is omitted. In FIG. 12A, a laser light 108 (solid line) emitted from the light guiding plate 102 is deflected in the traveling direction by the deflecting unit 105, transmits through the liquid crystal panel 101 and enters one pupil (pupil 110L of the left eye in FIG. 12A) of the observer. The laser light 109 (dotted line) is also deflected in the traveling direction by the deflecting unit 105, transmits through the liquid crystal panel 101 and enters the one pupil (pupil 110L of the left eye in FIG. 12A) of the observer.
As shown with the solid line (laser light 108) and the dotted line (laser light 109) in FIG. 12A, each laser light that transmits through different areas of the liquid crystal panel 101 is deflected in different directions, and is controlled to enter one pupil (pupil 110L of the left eye in FIG. 12A) of the observer. The laser light that transmits through the liquid crystal panel 101 is a diffused light, and an image can be recognized by observing the diffused light that transmits through each pixel of the liquid crystal panel 101. In other words, as FIG. 12A shows, the laser light that transmits through each pixel of the liquid crystal panel 101 spreads somewhat when it reaches the pupil.
Patent Document 1: US Patent Application Publication No. 2010/0259604